US20220145086A1 - Methods of preparing structural colorants - Google Patents

Methods of preparing structural colorants Download PDF

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US20220145086A1
US20220145086A1 US17/438,396 US202017438396A US2022145086A1 US 20220145086 A1 US20220145086 A1 US 20220145086A1 US 202017438396 A US202017438396 A US 202017438396A US 2022145086 A1 US2022145086 A1 US 2022145086A1
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particles
photonic
calcining
polymer
metal oxide
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Zenon Paul Czornij
Charles L. Tazzia
Paragkumar Thanki
Elijah Shirman
Theresa M. KAY
Joanna Aizenberg
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BASF Coatings GmbH
Harvard College
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BASF Coatings GmbH
Harvard College
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Assigned to BASF CORPORATION reassignment BASF CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: TAZZIA, CHARLES L., CZORNIJ, ZENON PAUL
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C3/00—Treatment in general of inorganic materials, other than fibrous fillers, to enhance their pigmenting or filling properties
    • C09C3/006—Combinations of treatments provided for in groups C09C3/04 - C09C3/12
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G49/00—Compounds of iron
    • C01G49/02—Oxides; Hydroxides
    • C01G49/08—Ferroso-ferric oxide [Fe3O4]
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/22—Compounds of iron
    • C09C1/24—Oxides of iron
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C09C1/3009—Physical treatment, e.g. grinding; treatment with ultrasonic vibrations
    • C09C1/3027—Drying, calcination
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C09C1/3009—Physical treatment, e.g. grinding; treatment with ultrasonic vibrations
    • C09C1/3036—Agglomeration, granulation, pelleting
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C09C1/3072—Treatment with macro-molecular organic compounds
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    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C09C1/309—Combinations of treatments provided for in groups C09C1/3009 - C09C1/3081
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C3/00—Treatment in general of inorganic materials, other than fibrous fillers, to enhance their pigmenting or filling properties
    • C09C3/04—Physical treatment, e.g. grinding, treatment with ultrasonic vibrations
    • C09C3/043—Drying, calcination
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C3/00—Treatment in general of inorganic materials, other than fibrous fillers, to enhance their pigmenting or filling properties
    • C09C3/04—Physical treatment, e.g. grinding, treatment with ultrasonic vibrations
    • C09C3/045—Agglomeration, granulation, pelleting
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C3/00—Treatment in general of inorganic materials, other than fibrous fillers, to enhance their pigmenting or filling properties
    • C09C3/10—Treatment with macromolecular organic compounds
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
    • C09D7/40—Additives
    • C09D7/60—Additives non-macromolecular
    • C09D7/61—Additives non-macromolecular inorganic
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/18—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
    • C01P2002/84—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by UV- or VIS- data
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/30—Particle morphology extending in three dimensions
    • C01P2004/32—Spheres
    • C01P2004/34—Spheres hollow

Definitions

  • Structural colorants exhibit color via light interference effects, relying on physical structure as opposed to chemical structure.
  • Structural colorants are found in nature, for instance in bird feathers, butterfly wings and certain gemstones.
  • Structural colorants are materials containing microscopically structured surfaces small enough to interfere with visible light and produce color.
  • Structural colorants can be manufactured to provide color in various goods such as paints and automotive coatings.
  • manufactured structural colorants it is desired that the material exhibit high chromatic values, special photonic effects, dimensions allowing their use in particular applications, and chemical and thermal robustness.
  • the robustness of the material is important in order to allow their in-process stability in paint systems and under various natural weathering conditions.
  • One or more of the above objects and others can be achieved by virtue of the present invention which in certain embodiments is directed a method of preparing structural colorants comprising photonic particles, the method comprising varying the calcination temperature in the process to enable the tuning of pore size to obtain a wide variety of possible colors.
  • inventions are directed to a method of preparing structural colorants comprising photonic particles, the method comprising varying the calcination temperature in the process to enable the tuning of carbon black within the particles to obtain a wide variety of possible colors.
  • the structural colorants according to any of the above embodiments can be, e.g., selected from the group consisting of photonic spheres, photonic crystals, photonic granules, opals, inverse opals, folded photonic structures and platelet-like photonic structures.
  • FIG. 1A depicts the spectral properties of platelet-like materials calcined at different temperatures in presence of oxygen (under air).
  • FIG. 2 depicts the effect of the presence of oxygen on the appearance of platelet-like materials.
  • Pore size is typically controlled by the particle size of the colloid precursor use in creating the structure from which the inverse structure is derived after the thermal oxidation of the organic colloid particles. This essentially means that only one pore size (and hence one color position) can be made from a give colloid precursor.
  • the present invention in certain embodiments provides for diverse color range to be provided by a given colloid precursor.
  • the present invention is directed to a method of preparing structural colorants comprising photonic particles, the method comprising forming a liquid dispersion of polymer particles and a metal oxide; optionally forming droplets of the liquid dispersion; drying the droplets or the dispersion to provide polymer template particles comprising polymer particles and metal oxide; selecting a calcining parameter to remove the polymer particles from the template particles to achieve photonic particles comprising porous metal oxide particles having a pre-determined color that is correlated with the selection of the calcining parameter; and calcining the polymer template particles according to the selected calcining parameter to achieve the structural colorants comprising photonic particles.
  • This embodiment may further comprise selecting a different calcining parameter to remove the polymer particles from the template particles to achieve photonic particles comprising porous metal oxide microspheres having a different color.
  • the invention is directed to a method of preparing structural colorants comprising forming a liquid dispersion of polymer particles and a metal oxide; optionally forming droplets of the liquid dispersion; drying the droplets or the dispersion to provide polymer template particles comprising polymer particles and metal oxide; correlating two or more calcining parameters to remove the polymer particles from the template particles to provide photonic particles comprising porous metal oxide particles, to two or more different colors of the resultant particles; and calcining the polymer template particles according to one of the calcining parameters to achieve photonic particles of the correlated color to achieve the structural colorants comprising photonic particles.
  • This embodiment may also comprise calcining the polymer template particles according to different calcining parameters to achieve photonic particles of a different color.
  • the calcining parameter may be selected from, e.g., maximum temperature, time or a combination thereof.
  • the different maximum temperature is higher than the initial maximum temperature.
  • the different maximum temperature may be higher than the initial maximum temperature by at least about 25° C., at least about 50° C., at least about 75° C., or at least about 100° C. or by about 100° C., about 200° C., about 300° C., about 400° C. or about 500° C.
  • the different color is pushed toward the violet end of the visible spectrum as compared to the initial color.
  • the different maximum temperature is lower than the initial maximum temperature.
  • the different maximum temperature may be lower than the initial maximum temperature by at least about 25° C., at least about 50° C., at least about 75° C., or at least about 100° C. or by about 100° C., about 200° C., about 300° C., about 400° C. or about 500° C.
  • the different color is pushed toward the red end of the visible spectrum as compared to the initial color.
  • the reflective spectra of the initial photonic particles has a wavelength range selected from the group consisting of 380 to 450 nm, 451-495 nm, 496-570 nm, 571 to 590 nm, 591, 620 nm and 621 to 750 nm.
  • the reflective spectra of the second photonic particles has a wavelength range selected from the group consisting of 380 to 450 nm, 451-495 nm, 496-570 nm, 571 to 590 nm, 591, 620 nm and 621 to 750 nm and is a different wavelength of the initial photonic particles.
  • the present invention is directed to structural colorants comprising a metal oxide that are prepared in accordance with the methods disclosed herein,
  • Other embodiments are directed to liquid compositions comprising a liquid medium and the structural colorants disclosed herein; coatings comprising the structural colorants disclosed herein and articles of manufacture comprising a colorant comprising the structural colorants disclosed herein.
  • the structural colorants are selected from the group consisting of photonic spheres, photonic crystals, photonic granules, opals, inverse opals, folded photonic structures and platelet-like photonic structures.
  • the structural colorants are porous.
  • the structural colorants exhibit angle-dependent color or color independent color.
  • the structural colorants can be combined with one or more of a liquid medium, organic binders, additives, organic pigments, inorganic pigments or a combination thereof.
  • the metal oxide is selected from the group consisting of silica, titania, alumina, zirconia, ceria, iron oxides, zinc oxide, indium oxide, tin oxide, chromium oxide and combinations thereof.
  • the liquid medium can be, e.g., an aqueous medium, an organic medium or a combination thereof.
  • the structural colorant particles can have, e.g., one or more of an average diameter of from about 0.5 ⁇ m to about 100 ⁇ m, an average porosity of from about 0.10 to about 0.80 and an average pore diameter of from about 50 nm to about 999 nm.
  • the particles can have, e.g., one or more of an average diameter of from about 1 ⁇ m to about 75 ⁇ m, an average porosity of from about 0.45 to about 0.65 and an average pore diameter of from about 50 nm to about 800 nm.
  • the structural colorants particle have an average diameter, e.g., of from about 1 ⁇ m to about 75 ⁇ m, from about 2 ⁇ m to about 70 ⁇ m, from about 3 ⁇ m to about 65 ⁇ m, from about 4 ⁇ m to about 60 ⁇ m, from about 5 ⁇ m to about 55 ⁇ m or from about 5 ⁇ m to about 50 ⁇ m; for example from any of about 5 ⁇ m, about 6 ⁇ m, about 7 ⁇ m, about 8 ⁇ m, about 9 ⁇ m, about 10 ⁇ m, about 11 ⁇ m, about 12 ⁇ m, about 13 ⁇ m, about 14 ⁇ m or about 15 ⁇ m to any of about 16 ⁇ m, about 17 ⁇ m, about 18 ⁇ m, about 19 ⁇ m, about 20 ⁇ m, about 21 ⁇ m, about 22 ⁇ m, about 23 ⁇ m, about 24 ⁇ m or about 25 ⁇ m.
  • an average diameter e.g., of from about 1 ⁇ m to about 75 ⁇ m, from
  • Alternative embodiments can have an average diameter of from any of about 4.5 ⁇ m, about 4.8 ⁇ m, about 5.1 ⁇ m, about 5.4 ⁇ m, about 5.7 ⁇ m, about 6.0 ⁇ m, about 6.3 ⁇ m, about 6.6 ⁇ m, about 6.9 ⁇ m, about 7.2 ⁇ m or about 7.5 ⁇ m to any of about 7.8 ⁇ m about 8.1 ⁇ m, about 8.4 ⁇ m, about 8.7 ⁇ m, about 9.0 ⁇ m, about 9.3 ⁇ m, about 9.6 ⁇ m or about 9.9 ⁇ m.
  • the structural colorant particles have an average porosity, e.g., of from any of about 0.10, about 0.12, about 0.14, about 0.16, about 0.18, about 0.20, about 0.22, about 0.24, about 0.26, about 0.28, about 0.30, about 0.32, about 0.34, about 0.36, about 0.38, about 0.40, about 0.42, about 0.44, about 0.46, about 0.48 about 0.50, about 0.52, about 0.54, about 0.56, about 0.58 or about 0.60 to any of about 0.62, about 0.64, about 0.66, about 0.68, about 0.70, about 0.72, about 0.74, about 0.76, about 0.78, about 0.80 or about 0.90.
  • Alternative embodiments can have an average porosity of from any of about 0.45, about 0.47, about 0.49, about 0.51, about 0.53, about 0.55 or about 0.57 to any of about 0.59, about 0.61, about 0.63 or about 0.65.
  • the structural colorant particles have an average pore diameter, e.g., of from any of about 50 nm, about 60 nm, about 70 nm, 80 nm, about 100 nm, about 120 nm, about 140 nm, about 160 nm, about 180 nm, about 200 nm, about 220 nm, about 240 nm, about 260 nm, about 280 nm, about 300 nm, about 320 nm, about 340 nm, about 360 nm, about 380 nm, about 400 nm, about 420 nm or about 440 nm to any of about 460 nm, about 480 nm, about 500 nm, about 520 nm, about 540 nm, about 560 nm, about 580 nm, about 600 nm, about 620 nm, about 640 nm, about 660 nm, about 680 nm, about 700 nm,
  • Alternative embodiments can have an average pore diameter of from any of about 220 nm, about 225 nm, about 230 nm, about 235 nm, about 240 nm, about 245 nm or about 250 nm to any of about 255 nm, about 260 nm, about 265 nm, about 270 nm, about 275 nm, about 280 nm, about 285 nm, about 290 nm, about 295 nm or about 300 nm.
  • the structural colorant particles can have, e.g., an average diameter of from any of about 4.5 ⁇ m, about 4.8 ⁇ m, about 5.1 ⁇ m, about 5.4 ⁇ m, about 5.7 ⁇ m, about 6.0 ⁇ m, about 6.3 ⁇ m, about 6.6 ⁇ m, about 6.9 ⁇ m, about 7.2 ⁇ m or about 7.5 ⁇ m to any of about 7.8 ⁇ m about 8.1 ⁇ m, about 8.4 ⁇ m, about 8.7 ⁇ m, about 9.0 ⁇ m, about 9.3 ⁇ m, about 9.6 ⁇ m or about 9.9 ⁇ m; an average porosity of from any of about 0.45, about 0.47, about 0.49, about 0.51, about 0.53, about 0.55 or about 0.57 to any of about 0.59, about 0.61, about 0.63 or about 0.65; and an average pore diameter of from any of about 220 nm, about 225 nm, about 230 nm, about 235 nm, about
  • the structural colorants can have, e.g., from about 60.0 wt % to about 99.9 wt % metal oxide, based on the total weight of the colorants. In other embodiments, the structural colorants comprise from about 0.1 wt % to about 40.0 wt % of one or more light absorbers, based on the total weight of the colorants.
  • the metal oxide is from any of about 60.0 wt %, about 64.0 wt %, about 67.0 wt %, about 70.0 wt %, about 73.0 wt %, about 76.0 wt %, about 79.0 wt %, about 82.0 wt % or about 85.0 wt % to any of about 88.0 wt %, about 91.0 wt %, about 94.0 wt %, about 97.0 wt %, about 98.0 wt %, about 99.0 wt % or about 99.9 wt % metal oxide, based on the total weight of the structural colorants.
  • the structural colorant is prepared by a process comprising forming a liquid dispersion of polymer particles and a metal oxide; optionally forming liquid droplets of the dispersion; drying the liquid droplets or dispersion to provide polymer template particles comprising polymer particles and metal oxide; and removing the polymer particles by calcination as disclosed herein from the template particles to provide the porous metal oxide particles.
  • the structural colorant is prepared by a process comprising forming a dispersion of polymer particles and a metal oxide in a liquid medium; evaporating the liquid medium to obtain polymer-metal oxide particles; and calcining the particles as disclosed herein to obtain the photonic structures.
  • evaporating the liquid medium is in the presence of self-assembly substrates such as conical tubes or photolithography slides.
  • the particles may be, e.g., spherical or platelet-like and/or porous and/or monodisperse.
  • the structural colorants are prepared by a process comprising forming a liquid dispersion of monodisperse polymer particles and metal oxide; forming at least one further liquid solution or dispersion comprising monodisperse polymer nanoparticles; mixing each of the solutions or dispersions together; optionally forming droplets of the mixture; and drying the droplets or dispersion by calcination as disclosed herein to provide polymer particles that are polydisperse when the average diameters of the monodisperse polymer particles of each of the dispersions are different.
  • the particles are spherical or platelet-like and/or porous.
  • the structural colorants may be recovered, e.g., by filtration or centrifugation.
  • the drying comprises microwave irradiation, oven drying, drying under vacuum, drying in the presence of a desiccant, or a combination thereof.
  • the droplets are formed with a microfluidic device.
  • the microfluidic device can contain a droplet junction having a channel width, e.g., of from any of about 10 ⁇ m, about 15 ⁇ m, about 20 ⁇ m, about 25 ⁇ m, about 30 ⁇ m, about 35 ⁇ m, about 40 ⁇ m or about 45 ⁇ m to any of about 50 ⁇ m, about 55 ⁇ m, about 60 ⁇ m, about 65 ⁇ m, about 70 ⁇ m, about 75 ⁇ m, about 80 ⁇ m, about 85 ⁇ m, about 90 ⁇ m, about 95 ⁇ m or about 100 ⁇ m.
  • the wt/wt ratio of polymer particles to the metal oxide is from about 0.5/1 to about 10.0/1. In other embodiments, the wt/wt ratio is from any of about 0.1/1, about 0.5/1, about 1.0/1, about 1.5/1, about 2.0/1, about 2.5/1 or about 3.0/1 to any of about 3.5/1, about 4.0/1, about 5.0/1, about 5.5/1, about 6.0/1, about 6.5/1, about 7.0/1, about 8.0/1, about 9.0/1 or about 10.0/1.
  • the polymer particles have an average diameter of from about 50 nm to about 990 nm. In other embodiments, the particles have an average diameter of from any of about 50 nm, about 75 nm, about 100 nm, about 130 nm, about 160 nm, about 190 nm, about 210 nm, about 240 nm, about 270 nm, about 300 nm, about 330 nm, about 360 nm, about 390 nm, about 410 nm, about 440 nm, about 470 nm, about 500 nm, about 530 nm, about 560 nm, about 590 nm or about 620 nm to any of about 650 nm, a bout 680 nm, about 710 nm, about 740 nm, about 770 nm, about 800 nm, about 830 nm, about 860 nm, about 890 nm, about 910 nm,
  • the polymer is selected from the group consisting of poly(meth)acrylic acid, poly(meth)acrylates, polystyrenes, polyacrylamides, polyethylene, polypropylene, polylactic acid, polyacrylonitrile, derivatives thereof, salts thereof, copolymers thereof and combinations thereof.
  • the polystyrenes can be, e.g., polystyrene copolymers such as polystyrene/acrylic acid, polystyrene/poly(ethylene glycol) methacrylate or polystyrene/styrene sulfonate.
  • the metal oxide is selected from the group consisting of silica, titania, alumina, zirconia, ceria, iron oxides, zinc oxide, indium oxide, tin oxide, chromium oxide and combinations thereof.
  • removing the polymer spheres from the template microspheres comprises calcination, pyrolysis or solvent removal.
  • the calcining of the template spheres can be, e.g., at temperatures of from about 300° C. to about 800° C. for a period of from about 1 hour to about 8 hours.
  • the structural colorants can be metal oxide particles (e.g., photonic balls or platelet-like) which may be prepared with the use of a polymeric sacrificial template.
  • metal oxide particles e.g., photonic balls or platelet-like
  • an aqueous colloid dispersion containing polymer particles and metal oxide is prepared, the polymer particles being, e.g., nano-scaled.
  • the aqueous colloidal dispersion is mixed with a continuous oil phase, for instance within a microfluidic device, to produce a water-in-oil emulsion.
  • Emulsion aqueous droplets are prepared, collected and dried to form particles (e.g., spheres) containing polymer particles (e.g., nanoparticles) and metal oxide.
  • the particles can be prepared by evaporation.
  • the polymer particles or spheres are then removed via calcination as disclosed herein to provide metal oxide-organic material particles or spheres that are, e.g., micron-scaled, and that contain a high degree of porosity with, e.g., nano-scaled pores.
  • the particles may contain uniform pore diameters as a result of the polymer particles being spherical and monodisperse.
  • the removal of the polymer particles form an “inverse structure” or inverse opal.
  • the particles prior to calcination are considered to be a “direct structure” or direct opal.
  • the above methodology can also be modified to provide crystals, granules or folded structures.
  • the metal oxide particles in certain embodiments are porous and can be advantageously sintered, resulting in a continuous solid structure which is thermally and mechanically stable.
  • microfluidic devices are for instance narrow channel devices having a micron-scaled droplet junction adapted to produce uniform size droplets connected to a collection reservoir.
  • Microfluidic devices for example contain a droplet junction having a channel width of from about 10 ⁇ m to about 100 ⁇ m.
  • the devices are for instance made of polydimethylsiloxane (PDMS) and may be prepared for example via soft lithography.
  • PDMS polydimethylsiloxane
  • An emulsion may be prepared within the device via pumping an aqueous dispersed phase and oil continuous phase at specified rates to the device where mixing occurs to provide emulsion droplets.
  • an oil-in-water emulsion may be employed.
  • Suitable template polymers include thermoplastic polymers.
  • template polymers are selected from the group consisting of poly(meth)acrylic acid, poly(meth)acrylates, polystyrenes, polyacrylamides, polyvinyl alcohol, polyvinyl acetate, polyesters, polyurethanes, polyethylene, polypropylene, polylactic acid, polyacrylonitrile, polyvinyl ethers, derivatives thereof, salts thereof, copolymers thereof and combinations thereof.
  • the polymer is selected from the group consisting of polymethyl methacrylate, polyethyl methacrylate, poly(n-butyl methacrylate), polystyrene, poly(chloro-styrene), poly(alpha-methyl styrene), poly(N-methylolacrylamide), styrene/methyl methacrylate copolymer, polyalkylated acrylate, polyhydroxyl acrylate, polyamino acrylate, polycyanoacrylate, polyfluorinated acrylate, poly(N-methylolacrylamide), polyacrylic acid, polymethacrylic acid, methyl methacrylate/ethyl acrylate/acrylic acid copolymer, styrene/methyl methacrylate/acrylic acid copolymer, polyvinyl acetate, polyvinylpyrrolidone, polyvinylcaprolactone, polyvinylcaprolactam, derivatives thereof, salts thereof, and combinations thereof.
  • polymer templates include polystyrenes, including polystyrene and polystyrene copolymers.
  • Polystyrene copolymers include copolymers with water-soluble monomers, for example polystyrene/acrylic acid, polystyrene/poly(ethylene glycol) methacrylate, and polystyrene/styrene sulfonate.
  • Present metal oxides include oxides of transition metals, metalloids and rare earths, for example silica, titania, alumina, zirconia, ceria, iron oxides, zinc oxide, indium oxide, tin oxide, chromium oxide, mixed metal oxides, combinations thereof, and the like.
  • the wt/wt (weight/weight) ratio of polymer nanoparticles to metal oxide is for instance from about 0.1/1 to about 10.0/1 or from about 0.5/1 to about 10.0/1.
  • the continuous oil phase comprises for example an organic solvent, a silicone oil or a fluorinated oil.
  • oil means an organic phase immiscible with water.
  • Organic solvents include hydrocarbons, for example, heptane, hexane, toluene, xylene, and the like, as well as alkanols such as methanol, ethanol, propanol, etc.
  • the emulsion droplets are collected, dried and the polymer is removed. Drying is performed for instance via microwave irradiation, in a thermal oven, under vacuum, in the presence of a desiccant or a combination thereof.
  • Polymer removal may be performed for example via calcination, pyrolysis or with a solvent (solvent removal).
  • Calcination is performed in some embodiments at temperatures of at least about 200° C., at least about 500° C., at least about 1000° C., from about 200° C. to about 1200° C. or from about 200° C. to about 700° C.
  • the calcining can be for a suitable period, e.g., from about 0.1 hour to about 12 hours or from about 1 hour to about 8.0 hours. In other embodiments, the calcining can be for at least about 0.1 hour, at least about 1 hour, at least about 5 hours or at least about 10 hours.
  • the calcining can be from any of about 200° C., about 350° C., about 400° C., 450° C., about 500° C. or about 550° C. to any of about 600° C., about 650° C., about 700° C. or about 1200° C. for a period of from any of about 0.1 h (hour), 1 h, about 1.5 h, about 2.0 h, about 2.5 h, about 3.0 h, about 3.5 h or about 4.0 h to any of about 4.5 h, about 5.0 h, about 5.5 h, about 6.0 h, about 6.5 h, about 7.0 h, about 7.5 h about 8.0 h or about 12 h.
  • a liquid dispersion comprising polymer particles and metal oxide is formed with an oil dispersed phase and a continuous water phase to form an oil-in-water emulsion.
  • the oil droplets may be collected and dried as are aqueous droplets.
  • the particles may be spherical or spherical-like and may be micron-scaled, for example having average diameters from about 0.5 microns ( ⁇ m) to about 100 ⁇ m.
  • the polymer particles employed as a template may also be spherical and nano-scaled and are monodisperse, having average diameters for instance from about 50 nm to about 999 nm.
  • the polymer particles may also be polydisperse by being a mixture of monodisperse particles.
  • the metal oxide employed may also be in particle form, which particles may be nano-scaled.
  • the metal oxide of the dispersion may be provided as metal oxide or may be provided from a metal oxide precursor, for instance via a sol-gel technique.
  • Pore diameters may range in some embodiments from about 50 nm to about 999 nm.
  • the average porosity of the present metal oxide particles may be relatively high, for example from about 0.10 or about 0.30 to about 0.80 or about 0.90.
  • Average porosity of a particle means the total pore volume, as a fraction of the volume of the entire particle. Average porosity may be called “volume fraction.”
  • a porous particle may have a solid core (center) where the porosity is in general towards the exterior surface of the particle (e.g., sphere). In other embodiments, a porous particle may have a hollow core where a major portion of the porosity is towards the interior of the particle (e.g., sphere). In other embodiments, the porosity may be distributed throughout the volume of the particle. In other embodiments, the porosity may exist as a gradient, with higher porosity towards the exterior surface of the particle and lower or no porosity (solid) towards the center; or with lower porosity towards the exterior surface and with higher or complete porosity (hollow) towards the center.
  • the average sphere diameter is larger than the average pore diameter, for example, the average sphere diameter is at least about 25 times, at least about 30 times, at least about 35 times, or at least about 40 times larger than the average pore diameter.
  • the ratio of average sphere diameter to average pore diameter is for instance from any of about 40/1, about 50/1, about 60/1, about 70/1, about 80/1, about 90/1, about 100/1, about 110/1, about 120/1, about 130/1, about 140/1, about 150/1, about 160/1, about 170/1, about 180/1 or about 190/1 to any of about 200/1, about 210/1, about 220/1, about 230/1, about 240/1, about 250/1, about 260/1, about 270/1, about 280/1, about 290/1, about 300/1, about 310/1, about 320/1, about 330/1, about 340/1 or about 350/1.
  • Polymer template particles comprising monodisperse polymer particles may provide, when the polymer is removed, metal oxide microspheres having pores that in general have similar pore diameters.
  • polydisperse polymer particles can be used wherein the average diameters of the particles are different.
  • polymer particles comprising more than one population of monodisperse polymer particles, wherein each population of monodisperse polymer particles has different average diameters.
  • the particles comprise mainly metal oxide, that is, they may consist essentially of or consist of metal oxide.
  • a bulk sample of the particles exhibits color observable by the human eye.
  • a light absorber may also be present in the particles, which may provide a more saturated observable color.
  • Absorbers include inorganic and organic pigments, for example a broadband absorber such as carbon black. Absorbers may for instance be added by physically mixing the particles and the absorbers together or by including the absorbers in the droplets to be dried. For carbon black, controlled calcination may be employed to produce carbon black in situ from polymer decomposition.
  • a present particle may exhibit no observable color without added light absorber and exhibit observable color with added light absorber.
  • the structural colorants of the present invention may be employed as colorants for example for aqueous formulations, oil-based formulations, inks, coatings formulations, foods, plastics, cosmetics formulations or materials or for medical applications.
  • Coatings formulations include for instance architectural coatings, automotive coatings or varnishes.
  • the structural colorants may exhibit angle-dependent color or angle-independent color.
  • Angle-dependent color means that observed color has dependence on the angle of incident light on a sample or on the angle between the observer and the sample.
  • Angle-independent color means that observed color has substantially no dependence on the angle of incident light on a sample or on the angle between the observer and the sample.
  • Angle-dependent color may be achieved for example with the use of monodisperse polymer spheres. Angle-dependent color may also be achieved when a step of drying the liquid droplets to provide polymer template spheres is performed slowly, allowing the polymer spheres to become ordered. Angle-independent color may be achieved when a step of drying the liquid droplets is performed quickly, not allowing the polymer spheres to become ordered.
  • the structural colorants may comprise from about 60.0 wt % (weight percent) to about 99.9 wt % metal oxide and from about 0.1 wt % to about 40.0 wt % of one or more light absorbers, based on the total weight of the particles.
  • the light absorber can be, e.g., from about 0.1 wt % to about 40.0 wt % of one or more light absorbers, for example comprising from any of about 0.1 wt %, about 0.3 wt %, about 0.5 wt %, about 0.7 wt %, about 0.9 wt %, about 1.0 wt %, about 1.5 wt %, about 2.0 wt %, about 2.5 wt %, about 5.0 wt %, about 7.5 wt %, about 10.0 wt %, about 13.0 wt %, about 17.0 wt %, about 20.0 wt % or about 22.0 wt % to any of about 24.0 wt %, about 27.0 wt %, about 29.0 wt %, about 31.0 wt %, about 33.0 wt %, about 35.0 wt %, about 37.0 w
  • particle size is synonymous with particle diameter and is determined for instance by scanning electron microscopy (SEM) or transmission electron microscopy (TEM). Average particle size is synonymous with D50, meaning half of the population resides above this point, and half below.
  • Particle size refers to primary particles. Particle size may be measured by laser light scattering techniques, with dispersions or dry powders.
  • Mercury porosimetry analysis can be used to characterize the porosity of the particles.
  • Mercury porosimetry applies controlled pressure to a sample immersed in mercury. External pressure is applied for the mercury to penetrate into the voids/pores of the material. The amount of pressure required to intrude into the voids/pores is inversely proportional to the size of the voids/pores.
  • the mercury porosimeter generates volume and pore size distributions from the pressure versus intrusion data generated by the instrument using the Washburn equation. For example, porous silica particles containing voids/pores with an average size of 165 nm have an average porosity of 0.8.
  • a bulk sample of particles means a population of particles.
  • a bulk sample of particles is simply a bulk population of particles, for instance ⁇ 0.1 mg, ⁇ 0.2 mg, ⁇ 0.3 mg, ⁇ 0.4 mg, ⁇ 0.5 mg, ⁇ 0.7 mg, ⁇ 1.0 mg, ⁇ 2.5 mg, ⁇ 5.0 mg, ⁇ 10.0 mg or ⁇ 25.0 mg.
  • a bulk sample of particles may be substantially free of other components.
  • the phrase “exhibits color observable by the human eye” means color will be observed by an average person. This may be for any bulk sample distributed over any surface area, for instance a bulk sample distributed over a surface area of from any of about 1 cm 2 , about 2 cm 2 , about 3 cm 2 , about 4 cm 2 , about 5 cm 2 or about 6 cm 2 to any of about 7 cm 2 , about 8 cm 2 , about 9 cm 2 , about 10 cm 2 , about 11 cm 2 , about 12 cm 2 , about 13 cm 2 , about 14 cm 2 or about 15 cm 2 . It may also mean observable by a CIE 1931 2° standard observer and/or by a CIE 1964 10° standard observer.
  • the background for color observation may be any background, for instance a white background, black background or a dark background anywhere between white and black.
  • microspheres may mean for example a plurality thereof, a collection thereof, a population thereof, a sample thereof or a bulk sample thereof.
  • micro or “micro-scaled” means from about 0.5 ⁇ m to about 999 ⁇ m.
  • nano or “nano-scaled” means from about 1 nm to about 999 nm.
  • the term “monodisperse” in reference to a population of particles means particles having generally uniform shapes and generally uniform diameters.
  • a present monodisperse population of particles for instance may have 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% of the particles by number having diameters within ⁇ 7%, ⁇ 6%, ⁇ 5%, ⁇ 4%, ⁇ 3%, ⁇ 2% or ⁇ 1% of the average diameter of the population.
  • Removal of a monodisperse population of polymer particles provides porous metal oxide particles having a corresponding population of pores having an average pore diameter.
  • substantially free of other components means for example containing ⁇ 5%, ⁇ 4%, ⁇ 3%, ⁇ 2%, ⁇ 1% or ⁇ 0.5% by weight of other components.
  • the articles “a” and “an” herein refer to one or to more than one (e.g. at least one) of the grammatical object. Any ranges cited herein are inclusive.
  • the term “about” used throughout is used to describe and account for small fluctuations. For instance, “about” may mean the numeric value may be modified by ⁇ 5%, ⁇ 4%, ⁇ 3%, ⁇ 2%, ⁇ 1%, ⁇ 0.5%, ⁇ 0.4%, ⁇ 0.3%, ⁇ 0.2%, ⁇ 0.1% or ⁇ 0.05%. All numeric values are modified by the term “about” whether or not explicitly indicated. Numeric values modified by the term “about” include the specific identified value. For example “about 5.0” includes 5.0.
  • Weight percent if not otherwise indicated, is based on an entire composition free of any volatiles, that is, based on dry solids content.
  • the photonic material prepared by the methods disclosed herein can have UV absorption functionality and can be coated on or incorporated into a substrate, e.g., plastics, wood, fibers or fabrics, ceramics, glass, metals and composite products thereof.
  • a substrate e.g., plastics, wood, fibers or fabrics, ceramics, glass, metals and composite products thereof.
  • the materials used in this example include: styrene (99%, Sigma-Aldrich Reagent Plus, with 4-ter-butylcatechol as stabilizer); 4-methoxyphenol (BISOMER S 20 W, GEO Specialty Chemicals); acrylic acid (Sigma-Aldrich); and ammonium persulfate (APS, OmniPur, Calbiochem).
  • a 500 ml three-neck round-bottom flask equipped with a water condenser, thermometer, nitrogen inlet, and magnetic stirrer was placed in an oil bath.
  • 129 ml of deionized water (18.2 Macm) was added and purged with nitrogen through a needle inserted into the reaction mixture while stirring at 300 rpm for 15 minutes.
  • Styrene (8.84 g, 84.8 mmol) was added under stirring and the flask was heated to 80° C. The needle delivering nitrogen was withdrawn from the reaction mixture yet left inside the flask to allow nitrogen flow through the flask for the duration of the reaction.
  • the materials used in this example include: ammonium persulfate (APS)—free-radical initiator; methyl methacrylate (MMA)—monomer; ethylene glycol dimethacrylate (EGDMA)—crosslinker; and 1-dodecanethiol—chain-transfer agent.
  • APS ammonium persulfate
  • MMA methyl methacrylate
  • EGDMA ethylene glycol dimethacrylate
  • 1-dodecanethiol chain-transfer agent.
  • the co-assembly solution is comprised of a mixture of a silica precursor solution and polymer colloids (PMMA or PS) suspended in water.
  • the silica precursor was prepared by combining tetraethylorthrosylicate (TEOS), ethanol, and 0.01 M HCl (1:1.5:1, v/v) and left to stir for 1 hour. 100 pl of the precursor solution was added to 20 ml water containing 0.1% colloids (w/v). Solutions were briefly sonicated (15 seconds) and then placed undisturbed in a 65° C. oven for 2-3 days, or until the liquid fully evaporated. Calcination was performed by ramping the temperature to at 500° C. for 5 hours, isothermal step for two hours, and ramp down for 4 hours. Typical yields were about 4 to 5 mg per 20 ml. Alterations in calcination conditions (temperature, ramping speeds, and oxygen-free environments) were also investigated.
  • a solution of TEOS was prepared in the following manner: 1000 ⁇ l of TEOS were added to a mixture containing 800 ⁇ l of methanol and 460 ⁇ l of water followed by 130 ⁇ l of a concentrated hydrochloric acid and 260 mg of cobalt nitrate dissolved in 160 ⁇ l of water. The opals were infiltrated with this solution in three repetitive steps, allowing for one hour drying in between each infiltration, to ensure substantial filling of the structure.
  • the material (compound opal) was calcined under argon or in the presence of air, using the following conditions: 10 min ramp to 65° C., hold for 3 hours (to allow for drying and, in the case of argon, to ensure removal of all oxygen from the system), ramp for two hours up to 650° C., hold for two hours and ramp down to room temperature for two hours. After calcination the final product was ground through two consecutive metal sieves, with 140 and 90 microns pore sizes respectively using ethanol to help transfer the powder through the meshes.
  • platelet-like structures were left for one hour in a 130° C. oven. Then the platelet-like structures were transferred into a vacuum desiccator containing three two-ml vials with 100 pl of 1H,1H,2H,2H-tridecafiuorooctyltrichlorosilane (13F) each for 48 h. Upon completion, the powder was placed in an oven at 130° C. for 15 min.
  • Calcination of platelet-like structures in inert conditions results in the deposition of carbon black within the pores of the inverse opal particles. Presence of the carbon black reduces the surface area of the silica accessible for reaction with silanes. Initial attempts to modify the particles with 13F in the gas or liquid phase as described above showed limited degree of surface modification resulting in water and organic solvents capable of infiltration into the pores. Consequently binding of perfluoroalkane to the carbon deposit was attempted. First, the surface of the carbon black was activated by stirring about 100 mg of platelet-like structures in a mixture of sulfuric and nitric acid (3 ml and 1 ml respectively) at 70° C. for two hours.
  • This activation step was aimed to form carboxylated surface on the carbon black. Following this activation step the platelet-like structures were washed in two rounds of centrifugation (8K RPM) and redispersion in 1M HCl followed by three rounds of centrifugation and redispersion in DI water. The resulted powder was transferred into a glass vial and allowed to dry in the oven at 65° C. for 4 hours. After drying the powder was redispersed in 1 ml of dichloromethane (DCM).
  • DCM dichloromethane
  • the aqueous dispersed phase was prepared by mixing 1 ml of colloidal dispersions (4.4 wt-%) with 0.5 ml of silica nanocrystals (5 wt-%). Emulsification of the aqueous mixture was performed using a T-junction dropmaker, with channels width of 50 micron, using Novec-7500 oil containing 0.5 wt-% triblock surfactant as a continuous phase. The emulsion was collected into 2 ml glass vials previously treated with 13F. Surface modification of the vials was performed by placing a plastic tray with 100 vials into a vacuum chamber containing 4 small plastic caps filled with 50 pl of the silane each.
  • the surface modification was required in order to avoid destabilization of the droplets upon contact with hydrophilic walls of the vial. Drying of the droplets was performed in a 45° C. oven or at RT occasionally shaking the container gently. The droplets are lighter than the oil phase prior to their complete drying and therefore have the tendency to float at the interface between the continuous phase and air and thus experiencing anisotropic drying environment. Thus, the shaking was done in order to minimize this effect. After complete drying, i.e. once the dispersed particles have no more tendency to float at the interface, an aliquot (20 pl) of photonic balls was deposited on a silicon substrate, calcined, and imaged using a Scanning Electron Microscope (SEM) and an optical microscope.
  • SEM Scanning Electron Microscope
  • the typical calcination conditions included temperature ramping up to 500° C. within 4 hours, isothermal stage for two hours and ramp down for four hours. Other calcination conditions were also studied, including faster ramp up and down (two hours each), variation in the temperature of the isothermal stage and presence of oxygen. Analogously to the results obtained with platelet-like structures, calcination of photonic balls at temperatures below 400° C. can result in incomplete removal of polystyrene colloids. Calcination at temperatures higher than 500° C. can cause shrinkage of the pores, and calcination in oxygen deficient conditions can result in the deposition of carbon black within the pores.
  • aqueous dispersion of silica colloids (10 wt-%) was emulsified in a similar manner as described above using a T-junction dropmaker, with channels width of 50 micron, using Novec-7500 oil containing 0.5 wt-% triblock surfactant as a continuous phase.
  • the emulsification was performed using a device with 100 micron channel opening. Stable formation of monodispersed droplets was performed at typical rates of 200-400 ⁇ l/hour for the continuous phase and 100-200 ⁇ l/hour for the dispersed phase for the T-junction device and 1-5 ml/hour for the continuous and dispersed phases for the device with 100 micron channel opening.
  • Free-form silica platelet-like photonic particles were fabricated according the procedure described above.
  • calcination temperature was measured at 300, 400, 500, 600 and 700° C.
  • the reflectance spectra of the products obtained from the calcination at various temperatures in the presence of air revealed a pronounced effect of the temperature on the peak wavelength of the final product ( FIG. 1B ).
  • Increasing the calcination temperature causes decrease in the final pore-size and a corresponding blue shift in the reflection spectrum.
  • Calcination of platelet-like materials in oxygen deficient conditions can result in the deposition of carbon black within the pores of platelet-like materials. Presence of carbon black enhances the contrast and substantially improves the visibility of platelet-like materials on white background as can be seen from the comparison of samples #3 and #4 in FIG. 2 .
  • Platelet-like materials samples #2 (templated using 270 nm polystyrene colloids, calcined at 700° C. under nitrogen), #3 (template using 240 nm poly(methylmethacrylate) colloids, calcined at 700° C. under nitrogen), and #4 (obtained from same batch as #3, but calcined at 500° C. under air) are shown in comparison to the pigment of the target blue color (sample #1).
  • the samples were deposited on stripes of transparent double-sided sticky tape and attached to the chart card. The samples are shown at diffuse lighting and the observance angle normal and 45 degrees with respect to the plane of the substrate.
  • the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X includes A or B” is intended to mean any of the natural inclusive permutations. That is, if X includes A; X includes B; or X includes both A and B, then “X includes A or B” is satisfied under any of the foregoing instances.
  • the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form.

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